Lead frame and semiconductor device

ABSTRACT

A lead frame for use with a plastic encapsulated semiconductor device includes a tab on which the semiconductor chip is mounted, chip pad supporting leads, inner leads to be electrically coupled with the semiconductor chip, outer leads formed in a monoblock structure together with the inner leads, and a frame for supporting the chip pad supporting leads and outer leads. In the lead frame, there is disposed a dam member only between the outer leads. Alternatively, dummy outer leads are formed between the frame and leads adjacent thereto so as to connect the dummy leads to the outer leads by the dam member. The frame is removed after the semiconductor device is assembled.

This application is a 37 CFR §1.60 divisional of prior application Ser.No. 08/438,467, filed May 10, 1995 now U.S. Pat. No. 5,637,914.

BACKGROUND OF THE INVENTION

The present invention relates to a technology of producing a lead frameand a technology of configuring a semiconductor device using the leadframe and, in particular, a technology effectively solving problemscaused by camber of the lead frame when a dam member is employed inplace of a dam bar.

Conventionally, a lead frame includes a dam bar fabricated with the samematerial together with the lead frame in a monoblock configuration. Thedam bar prevents encapsulation resin from flowing toward the outer leadside in the transfer mold process. Since the dam bar is integrallyformed in the lead frame, to achieve a cutoff process of the dam bar, itis necessary to conduct a cutting process using a metal mold.

However, recently, due to increasing tendency of capacity ofsemiconductor devices, the number of pins of a semiconductor devicepackage becomes greater, which necessitates a lead frame of a finerpitch construction having a lead pitch of 0.3 mm to 0.5 mm. This leadsto a technological problem that it is difficult to conduct the cuttingprocess of the dam bar by use of a metal mold. Even if the process isconducted, the production cost will be considerably increased. For thisproblem, to remove the cutoff process using a metal mold, there havebeen proposed methods of creating a dam bar in which, in place of theforming of the dam bar in the monoblock structure, an insulating tapeand a resin are used as members of the dam. Reference is to be made to,for example, the JP-A-58-28841, JP-A-2-122660, JP-A-310955, andJP-A-4-91464.

According to the methods above, the dam bar can be easily formed in amulti-pin lead frame and can be removed after the molding process in asimple process using, for example, an organic solvent. In addition,since the dam bar is fabricated with an insulating material, the processof removing the dam bar may possibly be dispensed with in some cases.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention, to provide a leadframe in a fine pitch configuration capable of considerably minimizingcamber of the lead frame by a dam bar including dam members and asemiconductor device using the lead frame.

Another object of the present invention is to provide a lead frame in afine pitch configuration capable of correctly achieving an outer leadmolding process and a semiconductor device using the lead frame.

According to the JP-A-58-28841, the dam bar is fabricated with aninsulating tape; whereas, various resins are employed according to theJP-A-2-122660, JP-A-310955, and JP-A-4-91464. The fabrication of the dambar on a lead frame using an insulating tape or resins requires apressurized molding process in a high temperature. Since the insulatingtape and resins generally have a coefficient of linear expansion largerthan that of materials of the lead frame (particularly, Fe--42Ni), theoverall lead frame disadvantageously cambers due to the difference inthe coefficient of linear expansion therebetween when an adhesive agentor resin is hardened on a surface of the tape.

FIG. 2 shows a conventional example of the lead frame constitutionaccording to the JP-A-58-28841 including a dam member 3 between an outerframe of lead frame 1 and an outer lead 2b adjacent thereto. When thedam member 3 is hardened and is contracted, the outer frame 1 is drawntoward the outer lead 2b connected thereto with the dam member 3. Sincethe outer frame 1 has higher rigidity, the contraction of the dam member3 cannot be absorbed by internal deformation of the outer frame,resulting in camber in the overall lead frame.

FIG. 3 shows the lead frame structure of another conventional exampleaccording to JP-A-4-91464 including a dam member 3 between a chip padsupporting lead 5 and an outer lead 2b adjacent thereto. Due to highrigidity of the supporting lead 5 with two supporting points, the leadframe is cambered through the similar mechanism as for the case of FIG.2. Camber in the lead frame disadvantageously causes peeling of a diebonding layer, deformation of the leads after a wire bonding process,and hindrance when transporting the lead frame in a semiconductormanufacturing process.

According to the present invention, there is provided a lead frame and asemiconductor device using the same in which occurrence of camber of thelead frame due to the dam bar formed with the dam member can beremarkably suppressed.

To achieve the objects according to the present invention, when a dambar is molded with an insulating dam member, only outer leads having lowrigidity are linked with each other by the dam member, namely, the outerframe of the lead frame and the chip pad supporting leads each havinghigher rigidity are not coupled with the dam member. Alternatively,between the outer frame or supporting leads and electric signal leadsfor electric conduction, there is arranged dummy leads at leastincluding only an outer lead (i.e. not including an inner lead) notrequiring electric conduction such that the dummy leads are connected tothe electric signal leads via the dam member. The dummy leads are cutaway after the resin molding process.

In short, the lead frame is configured as follows according to thepresent invention. In this specification, a term "dam" indicates amember for preventing, in a resin molding in which a cavity of a metalmold is filled with resin in a semiconductor manufacturing process, theresin from flowing from spaces between leads. Moreover, a term "tab"designates a portion on which a semiconductor chip formed in a leadframe surface is mounted, a term "inner lead" denote a lead portion(excepting the tab) in the resin, and a term "outer lead" represents alead portion outside the resin.

(1) A lead frame for use with a plastic encapsulated semiconductordevice includes a tab on which the semiconductor chip is mounted, chippad supporting leads to be connected to the tab, a plurality of innerleads to be electrically coupled with the semiconductor chip, outerleads formed in a monoblock structure together with the inner leads, aframe for supporting the chip pad supporting leads and the outer leadsand being cut away after the semiconductor device is assembled, and adam member made of an insulating material and disposed only between theouter leads for preventing a sealing resin from flowing out.

(2) A lead frame for use with a plastic encapsulated semiconductordevice includes a tab on which the semiconductor chip is mounted, chippad supporting leads to be connected to the tab, a plurality of innerleads to be electrically coupled with the semiconductor chip, outerleads formed in a monoblock structure together with the inner leads, aframe for supporting the chip pad supporting leads and the outer leadsand being cut away after the semiconductor device is assembled, and adam member made of an insulating material and disposed in a boundarybetween the inner leads and the outer leads for preventing a sealingresin from flowing out, the dam member being connected to the chip padsupporting leads or the frame at one position.

(3) A lead frame for use with a plastic encapsulated semiconductordevice includes a tab on which the semiconductor chip is mounted, chippad supporting leads to be connected to the tab, a plurality of innerleads to be electrically coupled with the semiconductor chip, outerleads formed in a monoblock structure together with the inner leads, aframe for supporting the chip pad supporting leads and the outer leadsand being cut away after the semiconductor device is assembled, and adam member made of an insulating material and disposed in a boundarybetween the inner leads and the outer leads for preventing a sealingresin from flowing out, the dam member being connected to the chip padsupporting leads or the frame at tow positions diagonal to each other.

(4) A lead frame for use with a plastic encapsulated semiconductordevice includes a tab on which the semiconductor chip is mounted, chippad supporting leads to be connected to the tab, a plurality of innerleads to be electrically coupled with the semiconductor chip, outerleads formed in a monoblock structure together with the inner leads, aframe for supporting the chip pad supporting leads and the outer leadsand being cut away after the semiconductor device is assembled, and adam member made of an insulating material and disposed in a boundarybetween the inner leads and the outer leads for preventing a sealingresin from flowing out, the dam member being connected to the chip padsupporting leads and the frame excepting at least at one position.

(5) A lead frame for use with a plastic encapsulated semiconductordevice includes a tab on which the semiconductor chip is mounted, chippad supporting leads to be connected to the tab, a plurality of innerleads to be electrically coupled with the semiconductor chip, outerleads formed in a monoblock structure together with the inner leads, aframe for supporting the chip pad supporting leads and the outer leadsand being cut away after the semiconductor device is assembled, dummyleads disposed between electric signal leads for electric conduction tothe semiconductor chip and the chip pad supporting leads or the frame,the dummy leads having no electric conduction to the semiconductor chipincluding at least only the outer leads, and a dam member made of aninsulating material and disposed in a continuous manner between theelectric signal leads and the dummy leads for preventing a sealing resinfrom flowing out.

(6) In a lead frame of item (5), the dummy leads are in an inner siderelative to a clamp outer edge clamped by a metal molding.

(7) In a lead frame of item (1), an insulating tape is fixed onto thedam forming portion and is then clamped at a high temperature, therebyforming a dam bar.

(8) In a lead frame of item (1), a resin is applied onto the dam formingportion by a dispenser and is then clamped at a high temperature,thereby forming a dam bar.

(9) In a lead frame of any one of the items (1) to (8), the outer leadshas a larger width in the dam member disposing portion.

(10) In a lead frame of any one of the items (1) to (9), the leads arearranged with a lead pitch less than 0.5 mm.

Furthermore, the semiconductor device of the present invention haseither one configurations.

(11) A semiconductor device is fabricated by mounting a semiconductorchip on a lead frame according to one of the items (1) to (10),electrically connecting the semiconductor chip to the lead frame, andencapsulating the semiconductor chip and the lead frame with a resin.

(12) A semiconductor device uses a lead frame for use with a plasticencapsulated semiconductor device including a tab on which thesemiconductor chip is mounted, chip pad supporting leads to be connectedto the tab, a plurality of inner leads to be electrically coupled withthe semiconductor chip, outer leads formed in a monoblock structuretogether with the inner leads, a frame for supporting the chip padsupporting leads and the outer leads and being cut away after thesemiconductor device is assembled, and a dam member made of aninsulating material for preventing a sealing resin from flowing out,wherein the dam member is in the periphery of the outer leads but is notat least at one position in the periphery of the chip pad supportingleads undergone the cutting process.

(13) In a semiconductor device of item (12), flatness of an outer edgeof the inner leads undergone the wire bonding process is at most 100 μm.

(14) In a semiconductor device using the lead frame of item (8), the dammember is removed after the semiconductor device is assembled.

(15) A semiconductor device uses a lead frame for use with a plasticencapsulated semiconductor device comprising a tab on which thesemiconductor chip is mounted, chip pad supporting leads to be connectedto the tab, a plurality of inner leads to be electrically coupled withthe semiconductor chip, outer leads formed in a monoblock structuretogether with the inner leads, a frame for supporting the chip padsupporting leads and the outer leads and being cut away after thesemiconductor device is assembled, and a dam member made of aninsulating material for preventing a sealing resin from flowing out,wherein flatness of an outer edge of the inner leads undergone the wirebonding process is at most 100 μm.

According to the above means, the insulating dam member disposed betweenthe outer leads serves the function of the conventional dam barfabricated in the monoblock structure together with the lead. Moreover,in the lead frame, since the dam of resin is not extended to the outerframe thereof, the deformation in the outer region is prevented andhence there can be remarkably minimized the camber of the lead frame dueto the dam member, thereby solving the problems related to occurrence ofthe camber.

Furthermore, there is provided a lead frame and a semiconductor deviceusing the same in which the outer lead molding process can beappropriately carried out with the same molding jigs as those used inthe prior art.

That is, another object of the present invention is achieved byemploying an outer lead bending process in which a portion of the leadthus bent has a narrow width and a minimized thickness.

According to the present invention, there is provided a lead frame foruse with a plastic encapsulated semiconductor device generally includinga rectangular and planar tab for mounting thereon a semiconductor chip,an outer frame for supporting the tab by chip pad supporting leads fromfour directions, groups of inner leads being laterally arrangedrespectively corresponding to four edges of the tab and extendingoutward from positions near the edges, groups of outer leads beinglinked with the inner leads and extending outward to be coupled with theouter frame, and a dam member made of resin connecting the laterallyarranged outer leads to each other. When molding the dam member, onlythe outer leads are coupled with each other by the dam member, namely,the outer frame or chip pad supporting leads having high rigidity is orare not connected thereto. Consequently, when the resin is hardened,deformation of the dame member is absorbed by the outer leads having lowrigidity to suppress deformation of the entire lead frame. Furthermore,when bending the outer leads, the width and thickness of the bentportion thereof is minimized for facilitating the forming process. Next,description will be given in detail of the present invention.

To achieve the object, a first lead frame of the present invention is alead frame for a plastic encapsulated semiconductor device including arectangular and planar tab for mounting on a surface thereof asemiconductor chip, chip pad supporting leads being connectedrespectively four corners of the tab and extending outward, an outerframe coupled with outer ends of the respective chip pad supportingleads for supporting the tab from four directions, groups of inner leadsbeing laterally arranged respectively corresponding to four edges of thetable and extending outward from positions near the edges, groups ofouter leads linked with outer ends of the inner leads and extendingoutward to be coupled with the outer frame, and an insulating dam memberconnecting only the outer leads to each other for each group thereof inthe proximity of a boundary between the inner leads and the outer leads,thereby filling gaps between the adjacent outer leads with the dammember. Moreover, in a portion of each of the outer leads in an area inwhich the dam member is arranged, there is disposed a narrow portionhaving a reduced lead width.

Moreover, like the first lead frame, a second lead frame of the presentinvention is a lead frame for a plastic encapsulated semiconductordevice including the components such as a tab, chip pad supportingleads, an outer frame, inner leads, and outer leads. There is disposedan insulating dam member connecting only the outer leads to each otherfor each group thereof in the proximity of a boundary between the innerleads and the outer leads, thereby filling gaps between the adjacentouter leads with the dam member. Moreover, there is arranged anadditional dam member extending from the dam member connecting twoadjacent groups of outer leads to a chip pad supporting lead existingtherebetween. Furthermore, in a portion of each of the outer leads in anarea in which the dam member is arranged, there is disposed a narrowportion having a reduced lead width. The additional dam member isarranged at one to three positions.

Additionally, like the first lead frame, a third lead frame of thepresent invention includes the components such as a tab, chip padsupporting leads, an outer frame, inner leads, and outer leads. There isfurther disposed dummy leads on both adjacent sides of each of the chippad supporting leads and extending inward from the outer frame. There isdisposed an insulating dam member connecting in the vicinity of aboundary between the inner leads and the outer leads two dummy leads andone of the groups of outer leads enclosed by the dummy leads, gapsbetween the adjacent dummy leads and between the outer leads beingfilled with the insulating dam member. Furthermore, in a portion of eachof the outer leads in an area in which the dam member is arranged, thereis disposed a narrow portion having a reduced lead width.

In addition, there are disposed variations respectively of the first tothird lead frames of the present invention. In a portion of each outerlead in the area in which the dam member is disposed, it is favorable todispose before and after the narrow portion a wide portion having alarger lead width as the portion in the vicinity. Alternatively, inplace of the narrow portion, there may be disposed a thin portion havingthe same lead width and a smaller lead plate thickness as the portionexisting in the vicinity. In this situation, the thin portion isfavorably disposed by forming a depression on an upper surface of theouter lead.

In this connection, in the first to third lead frames and variationsthereof, the outer frame is a member to be cut away after thesemiconductor chip is connected to the inner leads by wires and thesemiconductor chip and the inner leads are molded with resin, whereasthe narrow portion having a smaller lead width is at a position wherethe bending process is effected after the outer frame is cut away.

To achieve the object above, there is provided a semiconductor deviceaccording to the present invention in which the semiconductor device ismounted on either one of the lead frames according to the presentinvention and in which the inner leads connected to the semiconductordevice by wires are encapsulated with a sealing resin. Moreover, theouter frame is cut away and the outer leads are bent at the narrowportion (or the thin portion).

According to the lead frame for use with a plastic encapsulatedsemiconductor device, a semiconductor device is mounted on the tab to beconnected to the inner leads by wires and then the portions of the tab,semiconductor device, and inner leads are covered by a metal mold. Thecavity of the mold is filled with liquid resin so as to encapsulate theportions. To prevent resin from flowing out from the cavity through gapsbetween the adjacent inner leads in this process, there is disposed adam member in the boundary between the inner and outer leads on theouter lead side. The leads to be conducted to the semiconductor devicevia wires include the inner leads are disposed in the sealing resin andthe outer leads are arranged outside the resin.

In each of the lead frames according to the present invention, theinsulating dam member disposed for the outer leads serves a functionsimilar to that of the dam bar conventionally formed together with thelead frame with the same material in a monoblock structure. Furthermore,since the dam member does not extend to the outer frame having higherrigidity, deformation of the applied dam member during hardening thereofis absorbed in the leads having low rigidity to resultantly suppress thedeformation of the overall lead frame. Since the camber of the leadframe due to the dam member can be remarkably minimized, it is possibleto solve the problems, for example, peeling and disconnection of wireconnecting portions.

According to the lead frame, after the encapsulating process, the outerframe is cut away and the outer leads are bent in the proximity of theencapsulation resin mold. In the lead frame of the present invention, inthe area in which the outer leads are disposed, the portion of the outerlead bending position is formed as a narrow portion having a small leadwidth or as a thin portion to reduce rigidity of the lead. Consequently,the outer leads for which the dam member is arranged can be easily bentat the same position as for the conventional lead frame and hence theouter leads can be molded into a contour equal to that of theconventional outer leads.

That is, according to the lead frame of the present invention, in thearea in which the dam member is disposed, the portion of the outer leadbending position is formed as a narrow portion having a reduced leadwidth or as a thin portion to minimize rigidity of the lead. Inconsequence, the outer leads can be easily bent at the same positionassociated with that of the conventional lead frame and hence the outerleads can be molded into the same shape as those of the conventionalproducts.

According to the present invention, it is possible to considerablyreduce occurrence of camber appearing in the entire lead frame when thedam bar is formed with a dam member including an insulating tape orresin. Moreover, since three-dimensional camber is prevented by formingthe dam only between the outer leads, there appears only two-dimensionaldeformation in the outer ends of inner leads. In consequence, the amountof deformation of the outer ends of inner leads can be easily estimatedaccording to the contour of the leads and a characteristic of the dammember, thereby efficiently preventing unsatisfactory wire bonding.Furthermore, when fabricating the dam bar with an insulation tape, it isnecessary to form the tape in the contour of a frame according to theinventions of the prior art as shown in FIG. 3. However, the process isunnecessary according to the present invention and hence the productioncost is lowered. According to the present invention, the outer leads arebent at a predetermined position. In accordance with the presentinvention, there can be obtained a fine pitch configuration having afine pitch of 0.2 mm to 0.5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome apparent by reference to the following description andaccompanying drawings wherein:

FIG. 1A is a plan view of a lead frame as a first embodiment of thepresent invention;

FIGS. 1B and 1C are diagrams showing portions of cross sections of thelead frame of FIG. 1A;

FIG. 2 is a plan view of a lead frame using a conventional dam member;

FIG. 3 is a plan view of a lead frame using a conventional dam member;

FIG. 4 is a plan view of a lead frame as a second embodiment of thepresent invention;

FIG. 5 is a plan view of a lead frame as a third embodiment of thepresent invention;

FIG. 6 is a plan view of a lead frame as a fourth embodiment of thepresent invention;

FIG. 7A is a plan view of a lead frame as a fifth embodiment of thepresent invention;

FIG. 7B is magnified view for explaining a portion of a cross section ofthe lead frame of FIG. 7A;

FIG. 8 is a cross-sectional view of a semiconductor device as an eighthembodiment according to the present invention;

FIG. 9 is a top-surface view of a semiconductor device as a ninthembodiment according to the present invention;

FIG. 10 is a top-surface view of a semiconductor device as aconventional example;

FIG. 11 is a top-surface view of a semiconductor device as a tenthembodiment according to the present invention;

FIG. 12 is a cross-sectional view for explaining a position where a dammember is formed with resin according to the present invention;

FIG. 13 is a partially magnified view of the plan view of the lead frameof the sixth embodiment according to the present invention;

FIG. 14 is a magnified perspective view of the bending portion of thebase portion of the outer lead;

FIG. 15 is a partially magnified view of the plan view of the lead frameof the seventh embodiment according to the present invention;

FIG. 16 is a plan view partially showing a semiconductor device as aneighth embodiment of the present invention; and

FIG. 17 is a plan view showing an example of the molding of an outerlead.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A shows in a plan view a first embodiment of the lead frameaccording to the present invention.

The lead frame includes a tab 4 as a portion for mounting thereon asemiconductor chip, chip pad supporting leads 5, inner leads 2a, andouter leads 2b continuously connected to the inner leads, a dam member 3is formed in a boundary between the inner leads 2a and the outer leads2b in which the dam bar has been disposed in the monoblock structure,thereby connecting the outer leads 2b to each other by the dam member 3.

The dam member 3 is not formed in a continuous fashion with respect toan outer frame 1 of the lead frame or the supporting leads 5. Namely,the dam member 3 is disposed only to connect the outer leads 2b to eachother and is separated from the outer frame 1 of the lead frame or thesupporting leads 5. However, it is not necessary to separate allconnected portions, namely, the separating portions need only be decidedaccording to products.

Resin flows into a portion (burr) of FIG. 1A in the molding step.However, the resin can be easily removed therefrom when the supportingleads 5 are cut off or when the leads are bent. Since contraction in thehardening phase of the dam member 3 formed only between the outer leads2b is absorbed by the internal deformation between the outer leads 2b,the camber of the lead frame can be remarkably minimized when comparedwith the conventional structure.

The dam member used in the present invention can be selected from thegroup including an insulating epoxy resin, BT resin, phenole resin,polyimid resin, isomeran resin, silicone resin, any thermosetting resinproduced with a plurality of above resins or any thermoplastic resinsuch as aromatic polyetheramid, plyetheretherketone, polysulfone,aromatic plyesterimid, polyester, and (circulation) polyimid. When usingan insulating tape, it is possible to fix an insulation film with theabove material so as to clamp the insulation film at a high temperature.

When forming the dam member 3, a lead frame material is formed into apredetermined pattern by pressing or etching such that the resin isapplied by a dispenser only to spaces between the outer leads 2b in theportion in which the dam bar is conventionally arranged. The resin isthen heated and formed under pressure by a clamp. As can be seed fromthe cross section taken along line AA' of FIG. 1A, the dam portion isconfigured to enclose the outer leads 2b. FIGS. 1B and 1C show cases inwhich the resin is applied onto only one surface and both surfaces,respectively. The resin is applied to the surface, for example, bypotting or stamping. In this operation, when a resin having highviscosity is applied onto a rear surface of the lead frame, it ispossible to prevent the resin from flowing onto the front surfacethereof and hence there is attained an appropriately finished product.In FIG. 1A of the present invention, the dam member 3 is discontinuousat four positions. However, the advantageous effect of the presentinvention can be attained only with one discontinuous portion of the dammember 3.

In this regard, the dam member is disposed at a position as shown inFIG. 12. Namely, the lead frame member 26 is interposed between an upperpiece 22 of the metal mold and a lower piece 23 thereof such that resin25 is injected into a cavity 24 configured in the metal mold. Centeredon a portion at which the upper piece 22 is brought into contact withthe lower piece 23, there is established a resin dam zone 21 having arelatively large width.

FIG. 4 is a plan view showing a second embodiment of the lead frameaccording to the present invention.

Between leads (inner leads 2a and outer leads 2b) for electricconduction and an outer frame 1 of the lead frame, there are missinginner leads, namely, electric conduction is not provided. There arefabricated dummy outer leads 7 (to be referred to as dummy leadsherebelow), which are cut away after the resin molding process, suchthat boundary portions between the dummy outer leads 7 and adjacentinner leads 2a and outer leads 2b are filled with the dam member 3 tocouple the components with each other via the dam member 3 in the methoddescribed above.

The dummy outer leads 7 may be fabricated respectively in associationwith the outer frame 1 of the lead frame or either one of the endsthereof. The dummy outer leads 7 absorb contraction of the dam member 3in the contracting phase thereof to minimize the camber of the leadframe.

Additionally, in the first embodiment, it is required that the electricsignal leads in the corners are clamped by the metal mold when the resinmolding process is carried out without disposing the dummy leads 7. Incontrast therewith, according to the second embodiment, since the dummyleads 7 in the corners can be used as clamping surfaces, it is possibleto prevent defects and deformation due to the clamping of the electricsignal leads.

To prevent the resin from leaking out of the metal mold in the moldingprocess, in a portion 6 of FIG. 1A and in FIG. 4, the gaps between theouter frame 1 of the lead frame and the dummy leads 7 are required to beat an inner position relative to the outer end of portions clamped bythe metal mold.

FIG. 5 is a plan view showing a third embodiment of the lead frameaccording to the present invention. In an outer frame of the lead frame,there are formed slits 8 having an opening at an outer end thereof asshown in the diagram so as to form dummy leads 7a in an L shape in whichthe leads are bent by a right angle at an intermediate point thereof.The slit 8 is not limited to this shape if the dummy lead 7a can beformed in the bending structure. Boundary portions between the dummyleds 7a, inner leads 2a, and outer leads 2b are filled with the dammember 3 to link the components with each other in the molding methoddescribed above.

Like the first and second embodiments, this embodiment requires that theslits 8 are at an inner position relative to an outer end of clamp 12 tobe clamped by the clamp. However, since the dummy lead 7a is configuredin an L shape, the clamping area of the outer frame 1 of the lead framecan be considerably minimized when compared with the first and secondembodiments. Consequently, this efficiently prevents deformation andcamber of the lead frame due to the clamping.

FIG. 6 is a plan view showing a fourth embodiment of the lead frameaccording to the present invention. The leads of the first to thirdembodiments are arranged in two directions. Also in this case, the dammember 3 is disposed only between the outer leads 2b and is not broughtinto contact with the outer frame 1 of the lead frame.

FIG. 7 is a plan view showing a fifth embodiment of the lead frameaccording to the present invention. The width of outer leads 2b isenlarged only in the portion in which the dam member 3 is disposed so asto form wide lead portions 2c, thereby facilitating the applicationprocess of the dam member 3.

FIG. 14 is a magnified view of the plan view of the lead frame as asixth embodiment according to the present invention.

To enable a semiconductor device using a lead frame to be mounted on anactual printed circuit board after the molding process with sealingresin, there is employed a molding process of bending the outer leadsaccording to a predetermined contour. FIG. 17 shows an example of themolding process of the outer leads. Keeping by a retaining jig 15 alower surface 2b5 of a base portion (in the neighborhood of a packageside surface 14a) of an outer lead 2b, an upper surface of the outerlead 2b is pushed by a bending jig 16 so as to bend the outer lead 2bdownward at a bending position 2b2 in the vicinity of the side surface1a. As a result, the outer lead is bent as indicated by a referencenumeral 2b' in FIG. 17.

The bending position 2b2 of the outer lead 2b is apart from the packageside surface 14a by 0.1 mm to 0.3 mm and is in a portion in which thedam member is disposed. When the bending position 2b2 of the outer lead2b is in the portion in which the dam member is disposed, the baseportion of the outer lead has higher rigidity due to presence of the dammember. Consequently, the outer lead is bent as indicated by 2b" at aposition 3a in the outer end portion of the dam member, which leads to aproblem that the outer lead cannot be bent at the originally desiredbending position 2b2. Namely, when the outer leads of the lead frame inwhich the conventional dam bar is formed in the monoblock structure aremolded by the lead molding jigs, there arise problems that the outerleads after the molding process is different in contour from those ofthe conventional lead frames and hence flatness of the outer leadscannot be retained and the molding jigs are brought into contact withthe lead and plated coating is peeled from the leads and the moldingjigs are worn.

In a portion of the outer lead 2b in the area in which the dam member 3is disposed, there is formed a lead portion 2b1 having a narrow width asshown in the magnified view of FIG. 13. In this regard, the area inwhich the dam member 3 is arranged is indicated by broken lines. Thereduced-width portion 2b1 is employed to mount a semiconductor chip onthe lead frame and is substantially at a bending position 2b2 where theouter leads 2b processed with a sealing resin are bent in the moldingprocess. Namely, the position corresponds to the position 2b2 of FIG.17, indicating that the outer leads 2b are bent at the predeterminedposition.

Furthermore, thanks to the provision of the lead portion 2b1 having anarrow width in the portion of the outer lead 2b in the area where thedam member 3 is disposed, the outer lead has lower rigidity in the bentportion. Consequently, in the process of bending the outer lead 2b, itis possible to bend the outer lead 2b at a position equal to that of theconventional lead frame in which four dam bars are entirely coupled witheach other in a monoblock structure. Namely, the shape of the lead afterthe bending process is same as that of the conventional products. Inconsequence, the molding jigs adopted in the prior art can also beutilized; moreover, the problems occurring in the molding process can beprevented.

In addition, FIG. 14 shows a magnified perspective view of anotherexample of the bending portion in the base portion of the outer lead. Inthe bending position, the plate thickness is decreased to reducerigidity. In an area of the outer lead 2b including the bending position2b2 in the portion where the dam member 3 is arranged, there isfabricated a thin portion 2b3 having a reduced lead thickness. Thanks toprovision of the thin portion 2b3 as shown in FIG. 14, rigidity islowered in the bending position 2b2 of the outer lead 2b. Inconsequence, when forming the outer lead 2b, the outer lead 2b can bebent at the same position as that of the conventional lead frame inwhich dam bars are molded in a monoblock structure. The thin portion 2b3is molded by disposing a depression on one of or both of the surfaces ofthe outer lead 2b. The depression is disposed favorably in a surfaceupon which tensile stress acts when the outer lead 2b is bent, therebyreducing the thickness.

FIG. 15 is a diagram showing a seventh embodiment of the lead frameaccording to the present invention in which a portion of the lead wherethe dam member is disposed is magnified.

The dam member 3 is arranged in a portion including a boundary 2abbetween the outer lead 2b and the inner lead 2a. In FIG. 15, a zonewhere the dam member 3 is disposed is indicated by broken lines. In alead portion in which the dam member 3 is disposed, there is formed awide portion 2c having a larger lead width excepting a portion 2b of theouter lead 2b. The reduced-width portion 2b in the wide portion 2cmatches the lead bending position 2b2 in the bending process of theouter lead 2b after the resin molding process.

Thanks to provision that the wide portion 2c having a larger lead widthis manufactured in the portion where the dam member 3 is disposedexcepting the portion matching the bending position of the outer lead2b, the process of applying the dam member 3 can be facilitated.

FIGS. 16 and 8 show the eighth embodiment according to the presentinvention. FIG. 16 shows a state thereof prior to the lead bendingprocess of the lead frame in which the sealing resin is partiallyremoved. FIG. 8 is a cross-sectional view showing the contour of outerleads after the molding process.

Processes of fabricating a semiconductor device shown in FIGS. 16 and 8are as follows. On a tab 4 of the lead frame shown in FIGS. 1 and 4 to7, a semiconductor chip 9 is mounted with a die bonding agent and thenpredetermined areas respectively of the chip 9 and inner leads 2a areelectrically connected to each other by fine metallic wires 10. Inaddition, the lead frame is arranged in a metal mold and then a sealingresin 11 is supplied to the metal mold, thereby achieving a resinmolding process.

Thereafter, chip pad supporting leads 5 and burrs of resin remaining inthe periphery thereof are simultaneously cut away and then the outerleads 2b are cut and formed according to determined lengths, therebyobtaining a semiconductor device. According to the semiconductor devicethus fabricated using the lead frame of the present invention, since thecamber of the lead frame is remarkably minimized, flatness of the outerend portion of inner leads undergone the wire bonding process can be setto 100 μm or less required for reliability of wires.

FIG. 9 shows an upper-surface view of the semiconductor device thusproduced. In the periphery of the outer leads 2b in the outer-edgeportion of the sealing resin 11, there remains the dam member 3. Sincethe dam member 3 is formed to be separated from the chip pad supportingleads 5, the dam member 3 is missing in the periphery of the supportingleads 5 after the cutting process. However, as described in conjunctionwith the first embodiment, it is not necessary that the dam bar isformed to be separated from all chip pad supporting leads. Consequently,according to the present invention, it is also possible that the dammember 3 is missing in the periphery of at least one of the chip padsupporting leads in the obtained semiconductor device.

When a semiconductor device is fabricated with a lead frame according tothe conventional inventions, the resin dam and the like are formed inthe area where the conventional dam bar is disposed in the monoblockstructure. Consequently, a continuous portion of the remaining dammember 3 appears also between the chip pad supporting lead 5 undergonethe cutting process and the outer lead 2b adjacent thereto as shown inFIG. 10.

Furthermore, the dam portion is made of an insulating organic substance.In consequence, although there arises no problem in the state, the damportion can be easily removed by an organic solvent or the like.

FIG. 11 shows an upper-surface view of the semiconductor device in whichthe dam portion is removed. Since a portion of the dam member 3 is alsoformed in the resin molding process as shown in FIG. 8, when the damportion is removed by an organic solvent or the like, there appears agap 13 in the portion from which the dam portion is removed. In a caseof a semiconductor device using a lead frame according to the presentinvention, the gap 13 appears only in the periphery of the outer leads2b. In a case of a semiconductor device using a lead frame according tothe prior inventions, the dam member 3 of FIG. 10 is entirely removed.Consequently, it can be appreciated that the depression appears in acontinuous fashion between the chip pad supporting lead 5 undergone thecutting process and the outer lead 2b adjacent thereto.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by thoseembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

We claim:
 1. A method of manufacturing a lead frame including a tab formounting thereon a semiconductor chip, the tab having four edges in asubstantially rectangular contour, at least two chip pad supportingleads connected to the tab for supporting the tab, of leads includinginner leads and outer leads and having end surfaces being apart from atleast two edges of the four edges of the tab and opposing to each other,the chip pad supporting leads having an end connected only to an outerframe of the lead frame, and a dam member made of an insulating materialand disposed only between the outer leads for preventing a sealing resinfrom flowing out, comprising the steps ofmounting the semiconductor chipon the tab; and forming the dam member in a linear shape, the dam membertraversing the groups of leads and being apart from the chip padsupporting leads.
 2. A lead frame manufacturing method according toclaim 1, wherein the dam member fabricated by attaching a tape-shapedsubstance on at least one of two side surfaces of the groups of leads.3. A lead frame manufacturing method according to claim 1, wherein thedam member is fabricated by dropping or applying a liquid resin compoundon an upper surface and spaces between the groups of leads, the dammember traversing the groups of leads and being heated for hardeningthereof.
 4. A method of manufacturing a lead frame including a tab formounting thereon a semiconductor chip, the tab having four edges in asubstantially rectangular contour, chip pad supporting leads connectedto four corners of the tab and the outer frame, groups of leadsincluding inner leads and outer leads, and having end surfaces beingapart from side surfaces of the four edges of the tab and opposing toeach other, the chip pad supporting leads having an end connected onlyto an outer frame of the lead frame, and a dam member made of aninsulating material and disposed only between the outer leads forpreventing a sealing resin from flowing out,the method comprising thestep of mounting the semiconductor chip on the tab, and forming the dammember in a linear shape in association with each of the four edges, thedam member traversing the associated group of leads and being apart fromthe chip pad supporting leads.
 5. A lead frame manufacturing methodaccording to claim 4, wherein the dam member is fabricated by attachinga tape-shaped substance on at least one of two side surfaces of thegroups of leads.
 6. A lead frame manufacturing method according to claim4, wherein the dam member is fabricated by dropping or applying a liquidcompound on an upper surface and spaces between the groups of leads, thedam member traversing the groups of leads and being heated for hardeningthereof.
 7. A method of fabricating a semiconductor device using a leadframe according to claim 1, wherein when the lead frame is clamped by ametallic mold, outer edges of the clamp are on a surface of dummy leadsand along the dummy leads.
 8. A method of fabricating a lead frameaccording to claim 1, wherein an insulating tape is attached onto a damforming region and is clamped at a high temperature, thereby forming thedam member.
 9. A method of fabricating a lead frame according to claim1, wherein a resin is applied onto a dam forming region by a dispenserand is clamped at a high temperature, thereby forming the dam member.10. A method of fabricating a lead frame according to claim 4, whereinan insulating tape is attached onto a dam forming region and is clampedat a high temperature, thereby forming the dam member.
 11. A method offabricating a lead frame according to claim 4, wherein a resin isapplied onto a dam forming region by a dispenser and is clamped at ahigh temperature, thereby forming the dam member.
 12. A method ofmanufacturing a semiconductor device in which a semiconductor chip ismounted on a tab having four edges, at least two chip pad supportingleads extend from the tab to support the tab, groups of leads aredisposed including inner leads and outer leads, the leads having endsurfaces being apart from at least two edges of the four edges of thetab and opposing to each other, a dam member made of an insulatingmaterial and disposed only between the outer leads for preventing asealing resin from flowing out, conducting means connecting each of thegroups of leads to the semiconductor chips, wherein portions of each ofthe groups of leads on a tab side, the tab, the chip pad supportingleads, and the conducting means are sealed with a resin,the methodcomprising the following steps of:conducting a resin molding process inwhich a lead frame in which the chip pad supporting leads and the groupsof leads are connected to an outer frame of the lead frame is arrangedin a metallic mold, the semiconductor chip being mounted on the tab;forming the dam member in a linear shape, the dam member traversing eachof the groups of leads and being apart from the chip pad supportingleads; preventing a molding resin by the dam member and the metallicmold from flowing out from the metallic mold; and cutting away, afterremoval of the metallic mold, the outer frame of the lead frame.
 13. Alead frame according to claim 12, wherein the dam member is fabricatedby attaching a tape-shaped substance on at least one of two sidesurfaces of the groups of leads.
 14. A lead frame according to claim 12,wherein the dam member is fabricated by dropping or applying a liquidresin compound on an upper surface and spaces between the groups ofleads, the dam member traversing the groups of leads and being heatedfor hardening thereof.
 15. A method of fabricating a semiconductordevice comprising a tab mounting a semiconductor chip, a lead frameincluding leads comprising inner leads and outer leads including narrowportions having smaller widths respectively, and a dam member made of aninsulating material and disposed only between the outer leads forpreventing the insulating material from flowing out, said methodcomprising the steps of:mounting the semiconductor chip on the tab;molding the semiconductor chip and the tab by injecting the insulatingmaterial to an inner side of said dam member; and bending the narrowportions of the leads arranged at a position of the dam member forforming the outer leads of the leads.
 16. A method of fabricating asemiconductor device comprising a tab mounting a semiconductor chip alead frame including leads comprising inner leads and outer leadsincluding thick portions having larger thickness, respectively, and adam member made of an insulating material and disposed only between theouter leads for preventing the insulating material from flowing out,said method comprising the steps of:mounting the semiconductor chip onthe tab; molding the semiconductor chip and the tab by injecting theinsulating material to an inner side of said dam member; and bending thenarrow portions of the leads arranged at a position of the dam memberfor forming the outer leads of the leads.
 17. A method of manufacturinga lead frame including an outer frame, a tab for mounting thereon asemiconductor chip, at least two chip pad supporting leads connected tothe tab for supporting the tab, groups of leads including inner leadsand outer leads with the inner leads not being electrically connected tothe tab, and a dam member made of an insulating material and disposed toconnect only the outer leads for preventing a sealing resin from flowingout, comprising the steps ofmounting the semiconductor chip on the tab;and forming the dam member, the dam member traversing the groups ofleads and being apart from the chip pad supporting leads.
 18. A methodof manufacturing a lead frame including an outer frame, a tab formounting thereon a semiconductor chip, at least two chip pad supportingleads connected to the tab for supporting the tab, groups of leadsincluding inner leads and outer leads with the inner leads not beingelectrically connected to the tab, and a dam member made of aninsulating material and disposed to connect only the outer leads forpreventing a sealing resin from flowing out, with the dam member notconnecting any one of the outer frame and the at least two chip padsupporting leads with the outer leads, comprising the steps ofmountingthe semiconductor chip on the tab; and forming the dam member, the dammember traversing the groups of leads and being apart from the chip padsupporting leads.
 19. A method of manufacturing a lead frame includingan outer frame, a tab for mounting thereon a semiconductor chip, chippad supporting leads connected to the tab and the outer frame, groups ofleads including inner leads and outer leads, and with the inner leadsnot being electrically connected to the tab, and a dam member made of aninsulting material and disposed to connect only between the outer leadsfor preventing a sealing resin from flowing out,the method comprisingthe step of mounting the semiconductor chip on the tab, and forming thedam member, the dam member traversing groups of outer leads extending ina common direction.
 20. A method of manufacturing a lead frame includingan outer frame, a tab for mounting thereon a semiconductor chip, chippad supporting leads connected to the tab and the outer frame, groups ofleads including inner leads and outer leads, and with the inner leadsnot being electrically connected to the tab, and a dam member made of aninsulting material and disposed to connect only between the outer leadsfor preventing a sealing resin from flowing out, with the dam member notconnecting any one of the outer frame and the at least two chip padsupporting leads with the outer leads,the method comprising the step ofmounting the semiconductor chip on the tab, and forming the dam member,the dam member traversing groups of the outer leads extending in acommon direction.
 21. A method of manufacturing a semiconductor devicewhich utilizes an outer frame, a semiconductor chip mounted on a tab, atleast two chip pad supporting leads extend from the tab to the outerframe to support the tab, groups of leads are disposed including innerleads and outer leads with the inner leads not being electricallyconnected to the tab, a dam member made of an insulating material anddisposed only between the outer leads for preventing a sealing resinfrom flowing out, conducting means connecting each of the groups ofleads to the semiconductor chip, wherein portions of each of the groupsof leads on a tab side, the tab, the chip pad supporting leads, and theconducting means are sealed with a resin,the method comprising thefollowing steps of:conducting a resin molding process in which a leadframe in which the chip pad supporting leads and the groups of leads areconnected to an outer frame of the lead frame is arranged in a metallicmold, the semiconductor chip being mounted on the tab; forming the dammember, the dam member traversing each of the groups of leads;preventing a molding resin by the dam member and the metallic mold fromflowing out from the metallic mold; and cutting away, after removal ofthe metallic mold, the outer frame of the lead frame.
 22. A method ofmanufacturing a semiconductor device which utilizes an outer frame, asemiconductor chip mounted on a tab, at least two chip pad supportingleads extend from the tab to the outer frame to support the tab, groupsof leads are disposed including inner leads and outer leads with theinner leads not being electrically connected to the tab, a dam membermade of an insulating material and disposed only between the outer leadsfor preventing a sealing resin from flowing out, with the dam member notconnecting any one of the outer frame and the at least two chip padsupporting leads with the outer leads, conducting means connecting eachof the groups of leads to the semiconductor chip, wherein portions ofeach of the groups of leads on a tab side, the tab, the chip padsupporting leads, and the conducting means are sealed with a resin,themethod comprising the following steps of:conducting a resin moldingprocess in which a lead frame in which the chip pad supporting leads andthe groups of leads are connected to an outer frame of the lead frame isarranged in a metallic mold, the semiconductor chip being mounted on thetab; forming the dam member, the dam member traversing each of thegroups of leads; preventing a molding resin by the dam member and themetallic mold from flowing out from the metallic mold; and cutting away,after removal of the metallic mold, the outer frame of the lead frame.23. A method of fabricating a semiconductor device comprising a tabmounting a semiconductor chip, at least two chip pad supporting leadsconnected to the tab for supporting the tab, a lead frame includingleads comprising inner leads and outer leads including narrow portionshaving smaller widths respectively, with the inner leads not beingelectrically connected to the tab, and a dam member made of aninsulating material and disposed to connect only the outer leads forpreventing the insulating material from flowing out, said methodcomprising the steps of:mounting the semiconductor chip on the tab;molding the semiconductor chip and the tab by injecting the insulatingmaterial to an inner side of said dam member; and bending the narrowportions of the leads arranged at a position of the dam member forforming the outer leads of the leads.
 24. A method of fabricating asemiconductor device comprising a tab mounting a semiconductor chip, atleast two chip pad supporting leads connected to the tab for supportingthe tab, a lead frame including leads comprising inner leads and outerleads including narrow portions having smaller widths respectively, withthe inner leads not being electrically connected to the tab, and a dammember made of an insulating material and disposed to connect only theouter leads for preventing the insulating material from flowing out,with the dam member not connecting any one of the outer frame and the atleast two chip pad supporting leads with the outer leads, said methodcomprising the steps of:mounting the semiconductor chip on the tab;molding the semiconductor chip and the tab by injecting the insulatingmaterial to an inner side of said dam member; and bending the narrowportions of the leads arranged at a position of the dam member forforming the outer leads of the leads.
 25. A method of fabricating asemiconductor device comprising an outer frame, a tab mounting asemiconductor chip, at least two chip pad supporting leads connected tothe tab for supporting the tab, a lead frame including inner leads andouter leads including thick portions having larger thickness,respectively, with the inner leads not being electrically connected tothe tab, and a dam member made of an insulting material and disposed toconnect only the outer leads for preventing the insulating material fromflowing out, said method comprising the steps of:mounting thesemiconductor chip on the tab; molding the semiconductor chip and thetab by injecting the insulating material to an inner side of said dammember; and bending the thick portions of the leads arranged at aposition of the dam member for forming the outer leads of the leads. 26.A method of fabricating a semiconductor device comprising an outerframe, a tab mounting a semiconductor chip, at least two chip padsupporting leads connected to the tab for supporting the tab, a leadframe including inner leads and outer leads including thick portionshaving larger thickness, respectively, with the inner leads not beingelectrically connected to the tab, and a dam member made of an insultingmaterial and disposed only between the outer leads for preventing theinsulating material from flowing out, with the dam member not connectingany one of the outer frame and the at least two chip pad supportingleads with the outer leads, said method comprising the steps of:mountingthe semiconductor chip on the tab; molding the semiconductor chip andthe tab by injecting the insulating material to an inner side of saiddam member; and bending the thick portions of the leads arranged at aposition of the dam member for forming the outer leads of the leads.